A new interleaving eddy current array-based sensing film for fatigue crack quantification of bolted joints

Abstract

Fatigue crack quantification for bolted joints attracts much attention to determine the structural integrity for aircraft structures. In this paper, a new sensing film with interleaving eddy current array is proposed to evaluate the parameters of the hole-edge crack for single- or multiple-lap bolted joints. In this sensing film, the exciting layer is one coil throughout the hole wall which consists of a one-dimension rectangle coil array in the axial direction connecting in series, while the sensing layer is made up of two interleaving layers with a two-dimensional sensing coil array distributed in the circumferential and axial directions for each layer. Finite element simulation is conducted to study the effect of different crack parameters on the induced voltage of sensing coils. Simulation results reveal that the sensing film has no blind angle of crack detection but a strong capability of quantifying the crack angle, and the arctangent value of the ratio between interleaving coils can be used for estimating the crack angle. After the crack angle is estimated, induced voltages of sensing coils at this angle may be used to track the crack propagation in the axial or radial directions of the bolt hole. Experiments are conducted to verify the feasibility and effectiveness of the new sensing film to monitor the angle, depth, and length of the hole-edge crack of bolted joints.